CU more tham 3m. from meter in domestic property.

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17Frank13

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I am currently undertaking a distance learning course to become a Domestic Installer. I have a domestic installation where the meter is more than 3m. from the CU.Because of this the supplier will not allow the tails between meter and CU to be protected by their 60A. fuse. I have had to have installed a double pole isolation switch, having an 80A. fuse, next to the meter and a small CU next to the switch with an RCD to protect the tails between the new CU and the main CU. All tails are in 25 sq. mm. cable. The RCD in the new CU next to the meter is a Proteus type AC, 80A., 230V., RATED @ 0.03A, housed in a Marlanvil 92.04 CU. Recently pressed the test button on this RCD and nothing happened, so I tried again, this tim keeping the test button depressed. There was an alarming bang, but again, the RCD did not trip. It therefore appears the RCD is faulty and needs to be replaced. I understand, however that as this RCD is in series with other RCD's in the main CU, it should have a timer delay and thus be an 'S' type RCD. It appears that I cannot get a 30mA RCD as an S type and can only get a 100mA RCD, which, I understand, will not protect against shock, only fire. Can anyone advise me as to which RCD I should replace the faulty on with? I have asked my tutors and other electricians, but no-one seems to know. Some advice on this would be much appreciated.

 
Frank can I ask why you have installed an RCD unit at front end? 

How long have you been doing this course? Have you any qualifications other than this course? Whose domestic install are you working on? We tend to have stopped using the bang test sometime ago, what method of testing have you undertaken? 

 
Any tutors would be able to tell you that this install has several things wrong at a really basic level. 

Edit: You may want to change your training, as you clearly state you are distance learning a DI course. Therefore it's not likely that you have an indentured apprenticeship. 

 
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I am not an apprentice, there was no other box to register with. I have been with Trades Gateway for two years. The installation is in my own home and has been tested and signed off by a qualified electrician.

 
Thed.reason for the RCD protection between the isolation switch and the main CU is that muy understanding is that the tails from the isolation switch to the main consumer unit would have to be either in earthed steel conduit or SWA if they were not RCD protected.

 
Sorry frank, but I'm not buying this?? There's an element of discrepancy with what you write. 

If the install has been tested by a qualified electrician then 1) I'd hope that he'd know what he required, 2) as he's tested it then why not call him back if you think it's failed. 3) you state that you have spoken to electricians and none of them appear to know what you require, odd as you've had a qualified spark test it?? 

I think we ought to start again with some of the missing information please. 

 
The DNO will not allow tails >3M long to be protected by their 60A fuse, so they ask you to fit your own switch fuse with an 80A fuse in it.

Can anyone spot a problem?  which fuse do you think will blow first when there is a fault?

 
As regards the electrician who signed off the installation, I have indeed telephoned him and asked him about this. He said he would find out but has not yet come back to me. The problem with the 80A. fuse occurred to me and I asked my tutor and was advised that it did not require to be changed for a 60A fuse.

 
I've read on the forum that Proteus is not the best! Should I change the fuse in thisolation switch to a 60A fuse. I can't see any reason why not? And what should I replace The RCD with?

One further thing, The supplier connected the meter tails to the isolation switch and didn't raise any questions.

 
Can I come?

please

just.............begging 

So the electrician signed this all off as compliant with BS7671, you think it's wrong, your lecturer doesn't know your electrician doesn't know and you clearly don't know? Did the electrician come through trades gateway as well? 

 
As regards the electrician who signed off the installation, I have indeed telephoned him and asked him about this. He said he would find out but has not yet come back to me. The problem with the 80A. fuse occurred to me and I asked my tutor and was advised that it did not require to be changed for a 60A fuse.


Are you certain that the spark you are getting to sign this off is competent? 

 
The Electrician in question is very experienced and I had him on recommendation from a a competent retired builder. he is a man in his 50's and has been an electrician all his life. I am really seeking an answer as to what needs to be done to correct the situation.

 

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